1. Field
The embodiments described herein relate generally to linear accelerators. More particularly, the described embodiments relate to linear accelerators providing multiple operating modes.
2. Description
A linear accelerator produces electrons or photons having particular energies. In one common application, a linear accelerator produces a radiation beam used for medical radiation treatment. The beam may be directed toward a target area of a patient in order to destroy cells within the target area by causing ionizations within the cells or other radiation-induced cell damage.
Radiation treatment plans are designed to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. However, designers of a treatment plan assume that relevant portions of a patient will be in a particular position relative to a linear accelerator during delivery of the treatment radiation. If the relevant portions are not positioned exactly as required by the treatment plan, the goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved. More specifically, errors in positioning the patient can cause the delivery of low radiation doses to tumors and high radiation doses to sensitive healthy tissue. The potential for misdelivery increases with increased positioning errors.
Conventional imaging systems may be used to determine a patient position prior to treatment according to a particular radiation treatment plan. For example, a radiation beam is emitted by a linear accelerator, passes through a volume of the patient and is received by an imaging system. The imaging system generates a two-dimensional portal image of the patient volume, which can be used to determine whether the patient is in a position dictated by the particular treatment plan.
The foregoing imaging systems may be both ineffective and inefficient. For example, the radiation beam generated by a linear accelerator for imaging may deliver a dose rate that is significantly less than a dose rate used for radiation treatment, but other characteristics of the beam may be unsuitable for imaging. Moreover, no efficient systems exist for changing these characteristics such that the resulting beam is suitable for imaging.